My buddy's brewpub (where I sometimes help out) uses H-S kegs, and they are very easy to use -- and relatively easy to clean. What kind of parts do you need? I'm not sure what parts are replaceable, but unless the gaskets are leaking, I wouldn't worry about it too much.

As for the rubber stopper, I really really doubt that would hold the pressure in -- you'd probably get the stopper popping out and spewing beer all over the place. Also, once the keg is empty, how would you get the stopper out (assuming it stayed in place during dispensing)? At the brewpub, we drill the wooden bungs out, clean and sanitize the kegs, and then fill and put a new bung in.

You can try Sabco for parts -- I know they sell the kegs and they have bungs, but probably in boxes of 1000 or something like that. If all you need are bungs, then you might be able to pick some up at a local micro/brewpub -- H-S kegs tend to be popular with craft brewers. And, as much as I hate to mention it, St. Pat's may have parts/bungs/taps as well.

Sabco should have the tap heads as well. If you can't find them on the website, click on the e-mail link and Sabco Dan will take care of you. I've purchased a bunch of stuff from them and have always had good service.